Refrigeration apparatus with defrosting system

ABSTRACT

An improved defrosting system for use with refrigeration apparatus, particularly of the type used for frozen food storage. The apparatus uses a two stage compressor with interstage cooling. During the defrost cycle, the suction gas from the evaporator coil is directed through the compressor so that the operation is in parallel, with a portion of the gas being admitted to the suction side of both the high stage and the low stage of the compressor. This permits an increased volume of hot gas at a higher temperature to be supplied to the evaporator and greatly reduces the time required to defrost the coil.

nited States Patent 1 Ditzler Mar. 11, 1975 REFRIGERATION APPARATUS WITH DEFROSTING SYSTEM [75] Inventor: John L. Ditzler, York, Pa.

[73] Assignee: Borg-Warner Corporation, Chicago,

Ill.

[22] Filed: Jan. 2, 1974 [21] Appl. No.: 430,296

ACCUMULATO 3,234,753 2/1966 Quick 62/278 Primary Examiner-William J. Wye Attorney, Agent, or Firm Thomas B Hunter [57] ABSTRACT An improved defrosting system for use with refrigeration apparatus, particularly of the type used for frozen food storage. The apparatus uses a two stage compressor with interstage cooling. During the defrost cycle, the suction gas from the evaporator coil is directed through the compressor so that the operation is in parallel, with a portion of the gas being admitted to the suction side of both the high stage and the low stage of the compressor. This permits an increased volume of hot gas at a higher temperature to be supplied to the evaporator and greatly reduces the time required to defrost the coil.

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r0 \n g 0 10 REFRIGERATION APPARATUS WITH DEFROSTING SYSTEM BACKGROUND AND SUMMARY or THE INVENTION This invention relates generally to defrosting arrangements for refrigeration apparatus used in frozen food storage or cold room applications. In the past, it has been conventional to employ a two stage compressor to permit operation to 30F without exceeding safe operating temperatures when condensing with ambient air as high as 145F. The use of a two stage compressor, in combination with interstage cooling, reduces the discharge gas temperature without sacrificing performance.

Several problems have been involved with the use of two stage compressors in accordance with the foregoing system. For example, since the temperature of the discharge gas is reduced the heat available for hot gas defrosting is limited. In the present invention, it is proposed to convert the compressor operation from two stage, series flow, wherein discharge gas from the low stage, after cooling, is admitted to the suction side of the high stage portion ofthe compressor, to parallel operation in which suction gas is admitted to the suction side of both the high stage and the low stage. Appropriate piping and valving arrangements are described, including control systems.

BRIEF DESCRIPTION OF THE DRAWING The single FIGURE is a schematic diagrammatic representation of a refrigeration apparatus constructed in accordance with the principles of the present invention.

DETAILED DESCRIPTION OF THE INVENTION Referring now to the FIGURE, reference numeral designates a compressor having a low stage 12 and a high stage 14. In normal operation, discharge gas from the compressor flows to condenser 16, receiver 18, and subcooler to a flow-retarding unit 19 of the type described in US. Pat. No. 3,163,998. From unit 19 refrigerant flows to an expansion device 22 and the liquid refrigerant is then expanded into the evaporator 24, flowing back to the compressor through an accumulator 28.

With respect to the piping arrangement, line connects the discharge side of the high stage 14 to a sole noid valve 32. Line 34 continues the hot gas line leading from solenoid 32 to the inlet side ofair cooled condenser 16. The condensed refrigerant then flows through line 36, check valve 38 to receiver 18. Line 40 connects the receiver to the inlet side of the subcooler 20, which usually forms the lower section of the condenser. From the subcooler 20, the liquid refrigerant flows through line 40 to a T fitting 44 which provides a branch line 46 for interstage cooling, in a manner to be described below, and a branch line 48 passing through solenoid valve 50 to the liquid refrigerant line 52 on the inlet side of unit 19 and then through expansion device 22 to the evaporator 24. The suction gas from the evaporator 24 flows through line 54 to the accumulator and from the accumulator through line 56 to a second T fitting 58. One branch line 60 from T 58 flows to the suction side of the low stage 12; and the other branch line 62 is connected to a one-way valve 64, line 66, to a T 68. Line 70 leads from the discharge side of low stage 12 to a cross-flow fitting 74 which joins the low stage discharge with interstage cooling line 80. Line contains a one-way valve 82, connected to line 46, solenoid valve 84 and expansion valve 86. The expanded refrigerant mixes with the hot discharge gas from the low stage at fitting 74 and may be directed through line 76 and one-way valve 88 or continue through line 70, through valve 72 to a T fitting 68 and high stage suction line 92.

OPERATION Under normal operation solenoid valves 72, 84, 32 and 50 are open; and valve 98 is closed. Accordingly. suction gas from the evaporator flows through line 54 through the accumulator 28. From the accumulator, the gas flows through lines 56 and 6 0 to the low stage of the compressor. With valve 72 open, hot gas then flows through lines 70 and 92 to the inlet side of the high stage compressor, and then through line 30, solenoid valve 32, and line 34 to the condenser 16. The liquid refrigerant leaves the condenser and flows through line 36, one-way valve 38, receiver 18 and line 40 the subcooler 20. The subcooled refrigerant then flows through line 42 and is split into two streams, one flowing through line 46, one-way valve 82, solenoid 84 and expansion device 86 to mix with the gas leaving the low stage through line 70 at cross-flow connection 74. The other stream flows through line 48, solenoid 50 and liquid line 52 to the flow retarding unit 19.

Since unit 19 is described in considerable detail in the previously noted US. Pat. No. 3,163,998 it is not necessary to repeat such description, which is incorporated herein by reference. It is understood that such unit, which is optional in the present invention, permits the controlled flow of liquid refrigerant, condensed in the evaporator during defrosting, back to the compressor. Line 52 connects to a heat exchanger (not shown) in unit 19 and passes liquid through line 53 to expansion valve 22. Suction gas flows into unit 19 through line 55 and out through line 54. The defrost hot gas connection is shown at 57.

When on defrost solenoid valves 72, 84, 32 and 50 are closed; and valve 98 is open. In this case, the gas leaving the accumulator through line 56 splits into two streams: one at 60 flowing to the low stage suction and the other at 62, flowing through one-way valve 64 and joining line 92 at T fitting 68. From the low stage, the gas passes directly through line 76 through one-way valve 88 to fitting 90 where it joins line 30. At the same time the high stage takes refrigerant gas through line 92 and directs it into line 30 where it eventually mixes with the discharge from the low stage. The gas then passes through open solenoid valve 98 and line 59 where it is directed to the hot gas connection 57 at unit 19. The hot gas is then quickly effective to melt the frost on the coil returning to the compressor through the main suction line 54.

While this invention has been described in connection with a-certain specific embodiment thereof, it is to be understood that this is by way of illustration and not by way of limitation; and the scope of the appended claims should be construed as broadly as the prior art will permit.

What is claimed is:

1. A refrigeration system comprising: a compressor, a condenser, an expansion device and an evaporator all connected in closed-circuit, refrigerant flow relationship, said compressor having a low stage and a high stage; a valve in said interstage gas line; a branch line connecting said evaporator and said high stage, whereby upon closing of said valve, suction gas will flow through said low stage and said high stage in parallel; and means for cooling gas flowing through said in- 

1. A refrigeration system comprising: a compressor, a condenser, an expansion device and an evaporator all connected in closedcircuit, refrigerant flow relationship, said compressor having a low stage and a high stage; means for conducting refrigerant from said low stage to said high stage in series flow during refrigeration operation; a hot gas defrost line connecting said compressor to said evaporator; a hot gas line connecting said high stage to said condenser; a suction gas line connecting said evaporator and Said low stage; an interstage gas line connecting said low stage and said high stage; a valve in said interstage gas line; a branch line connecting said evaporator and said high stage, whereby upon closing of said valve, suction gas will flow through said low stage and said high stage in parallel; and means for cooling gas flowing through said interstage gas line. 